The present invention relates to data storage, and more particularly, to supporting tape-attached storage partitions using a storage controller.
In a data storage system, many different types of storage media may be utilized. Some of the more frequently used storage media include magnetic tape used with tape drives, hard disk drives (HDDs), and volatile or non-volatile random access memory (RAM). Typically, all the different storage media types when used in a converged solution are transparent to a user of the data storage system, as a virtualization engine masks the actual storage location and simply presents the data to the user utilizing a cache that stores data prior to being subsequently stored in other, more permanent locations. However, the virtualization engine then must efficiently manage where the data is stored across the various media types, in order to provide adequate system performance from a standpoint of cost, speed, accessibility, etc.
There are four different anticipated workload groups that will store data on the data storage system. “Disk cache only content” which includes content that only resides in cache within a specific cluster. Even when back-end magnetic tape is present, no copy will end up on the magnetic tape. Workloads that require quick, 100% cache-hit access and do not require an additional copy on magnetic tape fall into this anticipated workload group.
A next anticipated workload group is “primarily tape only content,” which include workloads where the disk cache simply acts as a pass through cache allowing content to be immediately or near immediately migrated to magnetic tape. The disk cache is only used as a temporary repository for host and/or replication access. Workloads that are rarely accessed and likely do not expire quickly fall into this anticipated workload group.
Another anticipated workload group is “disk cache and tape content,” which include workloads that are either too large to be entirely cache resident or need an extra layer of redundancy where a copy on magnetic tape is required. This copy on magnetic tape may exist in parallel with the copy in cache indefinitely. Workloads that require additional redundancy, need to be exported, or have an access pattern that provides a sufficient cache hit ratio when a portion exists in cache fall into this anticipated workload group.
Yet another anticipated workload group is “delayed to tape content,” which includes workloads that are capable of being moved to magnetic tape, but a premigration to magnetic tape only occurs after satisfaction of some rule (such as time since creation). When the rule is time based, this allows magnetic tape to become an “archive” target where only data which has aged long enough before expiring ends up on the magnetic tape.
Given the above four anticipated workload groups for a converged solution and their use cases, it becomes evident that it is difficult to manage the movement of data from the cache to the magnetic tape in an effective manner, either from a space management perspective or throughput (with cache hit ratio) perspective, depending on each individual workload.